1. Field of the Invention
The present invention relates generally to the field of wireless communication, and more particularly to a device and method for transmitting a reverse common channel message on a channel temporarily designated as dedicated (collision-free channel) in a multimedia communication system.
2. Description of the Related Art
In a communication system based on the TIA/EIA/IS-95 standard, messages are communicated between a base station (BS) and a mobile station (MS) generally on a forward paging channel and a reverse access channel which are common channels before a voice call is set up. For communication with a mobile station without a dedicated channel connection, the base station must transmit a message on the paging channel and receives a response on the access channel. From the mobile""s perspective, for communication with the base station without a dedicated channel connection, the mobile station transmits a message on the access channel and receives a response on the paging channel. There can be a plurality of paging and access channels. Each paging channel is distinguished by a unique Walsh code, and each access channel by a long code generated with an access channel long code mask.
FIGS. 1A and 1B illustrate message transmissions between a base station and a mobile station on common channels. Referring to FIG. 1A, when the base station transmits a control message on a paging channel, a corresponding addressed mobile station transmits a response message on an access channel. If the mobile station transmits a control message on the access channel, the base station transmits a response message to the mobile station on the paging channel. Referring to FIG. 1B, the mobile station sends an access channel message to the base station on the access channel after message exchange.
The conventional access channel communication method is suitable for processing a voice call with light traffic. If mobile stations sharing the same long code simultaneously transmit messages on the access channel, a message contention occurs, resulting in a loss of the messages. This mechanism is referred to as contention-based random access.
Upon such a message contention for the access channel, a mobile station should resume an attempt to transmit a message on the access channel. In this case, each mobile station transmits a message on the access channel using its assigned long code, and if the contention occurs, it perceives the message occurrence in a predetermined time and resumes a message transmission after a randomized time delay. The mobile station performs an initial attempt to access the base station at a predetermined power level. When it fails to receive an acknowledgement from the base station, it performs the next attempt at a power level a specified amount higher than the previous attempt. If repeated attempts to access the access channel for predetermined times turn out failures, the procedure starts again at the lowest predetermined power level. Information is transmitted on the access channel in access channel slots and access channel frames.
FIG. 8 describes a message transmission procedure on an access channel from a mobile station. The entire process of sending one message and receiving (or failing to receive) an acknowledgement for that message is called an access attempt. Each transmission in the access attempt is called an access probe. Access probes are a series of transmissions of progressively higher power used when a mobile first attempts to access the system. Each access probe is comprised of a preamble and a message capsule. Within an access attempt, access probes are grouped into access probe sequences. Each access probe sequence includes a predetermined number (Max_Probe_No) of access probes, and the entire access attempt is comprised of a predetermined number (Max_Sequence_No) of access probe sequences. The first access probe of each access probe sequence is transmitted at an initial, relatively low power level. Each subsequent access probe is transmitted at a progressively higher power level than the previous access probe. The time interval RS between access probe sequences is determined by a random function. The time interval TA+RT between access probes of an access probe sequence is also generated by a random function. After transmitting each access probe, the mobile station waits a predetermined period TA to receive an acknowledgement from the base station. If an acknowledgement is received, the access attempt ends successfully. If no acknowledgement is received, the next access probe is transmitted after a random time RT.
In the above long code sharing scheme for common channels, the mobile station uses a Hash function to determine a long code among all available long codes (access channel long codes) in its initialization state, so that all mobile stations fairly share the long codes for access channels. In order to assign mobile station classes, an average of an initial attempt time and a next attempt time is adjusted.
Depending upon whether data service is MS originated or BS originated, there are two types of messages sent on the access channel, i.e., a message sent autonomously by the mobile station and a response message which is a response to a base station (i.e., paging channel) message. The two messages are treated logically at an equal level. Both the MS initiated message and the page response message are transmitted using access channel long codes determined with the Hash function by the mobile station.
The transmission rate of the access channel is fixed in the conventional communication system. In accordance with the IS-95 standard, an access channel message is generated in accordance with upper layer and physical layer protocols. In addition, a message is spread by an access channel long code determined by the mobile station.
However, the mechanism of accessing common channels for data service in a conventional communication system has the following problems:
(1) Random accessxe2x80x94Because an access channel is acquired by the contention based random access, message transmissions with the same long code are likely to cause message contention, leading to message losses. When message contention occurs, a mobile station re-transmits a message on the access channel after a predetermined and randomized period. It is not possible to estimate the time required for acquisition of the access channel thereby increasing an average message transmission time, the variation of the transmission time, and power consumption of the mobile station;
(2) Long code sharingxe2x80x94The equal assignment of available long codes for common channels to mobile stations makes it impossible to control an individual probability of access channel contention for each mobile station. It is desirable, therefore, to apply different procedures of common channel access determined by the mobile station""s data requirements. That is, a mobile station entering a relatively less time-constrained data communication should have a different procedure of common channel access than a mobile station processing real time data like moving pictures. To do this, long codes should be assigned to the latter in such a way that it allows rapid access to a common channel, however, the conventional equal long code distribution method cannot afford this special data service;
(3) Mobile station class assignmentxe2x80x94It is impossible to assign mobile station classes in accessing a common channel because a contention probability cannot be controlled when the mobile stations is to use an access channel;
(4) A distinction cannot be made between control message initiating parts (MS initiation and BS initiation). That is, it is impossible to determine whether an access channel request priority should be given to a response message for a base station message over a message autonomously generated from a mobile station, or vice versa;
(5) A mobile can typically be classified by service priority, however, because of equal treatment of response messages for BS initiated messages, classes cannot be assigned to them; and
(6) The fixed transmission rate of the access channel: increases the transmission time of a long message on the access channel. The resulting increase in an access channel occupying time in turn increases the contention probability.
An object of the present invention, as embodied and broadly described herein, is to provide a device and method for communicating on common channels in a communication system, which can reduce the transmission delay of the common channels and increase the transmission efficiency thereof to support data service.
Another object of the present invention is to provide a common channel accessing device and method in a communication system, in which user classes are assigned depending on user data types in data communication.
A further object of the present invention is to provide a device and method for processing BS initiated data with a priority over MS initiated data in a communication system.
Still another object of the present invention is to provide a device and method for continuously transmitting a common channel message exceeding a one-time transmissible length on a designated specific common channel.
Yet another object of the present invention is to provide a device and method for spreading a reverse common channel message for transmission by a code assigned by a base station in order to prevent message contention.
To achieve the above objects, there is provided a common channel message communicating device and method in a CDMA communication system. In a base station of the common channel message communicating device, a control message generator generates a control message including information representative of a spreading code for spreading a reverse common channel message, and a forward common channel transmitter transmits the control message on a forward common channel. In a mobile station, a control message analyzer analyzes information representative of an assigned spreading code included in the control message received on the forward common channel, a spreading code generator generates a spreading code based on the spreading code information, and a channel transmitter spreads the reverse common channel message by the spreading code and transmits the spread reverse common channel message.